Update to the current master branch so that is has
cairo_user_font_face_set_render_color_glyph_func().
I had to disable optimized builds on win[32|64] crossbuild setups
because they are now broken in the CI (something about cairo defining
_FORTIFY_SOURCE for optimized builds that MingW does not like).
We don’t need it and it breaks the build because FontConfig renamed its
master branch and the released version of Cairo wants to build
FontConfig from master branch.
As a part of meson migration, this builds hb-shape dependencies
using meson subprojects and removes different unrelated mingw
files we've put on source root about things that aren't really our
concern. This also simplifies all the instructions we've put in
README.mingw.md and makes it easy to build the project on
distros that no mingw libraries (such i686-win32-{freetype,glib,...}
are packaged. The known catch is however lack of hb-view as its need
for build of cairo which apparently isn't that straightforward.